1. Field of the Invention
This invention relates to the making of flat glass by a continuous process wherein glass is formed as a continuous sheet while supported and conveyed along the surface of a pool of molten metal. More particularly, this invention relates to an improved method for initiating the delivery of molten glass from a glass melting and refining furnace to a glass forming chamber.
2. Description of the Prior Art
It is known to form flat glass by delivering molten glass over a refractory support onto the surface of a pool of molten metal and to thereafter cool it and form it into a continuous sheet of glass.
U.S. Pat. No. 710,357 to Heal and U.S. Pat. No. 789,911 to Hitchcock individually show the delivery of molten glass over a rigid refractory member and from that member directly onto the surface of molten metal in a forming chamber.
U.S. Pat. No. 3,083,501 to Pilkington shows the delivery of molten glass over a refractory member and thereafter permitting it to fall freely onto the surface of a pool of molten metal for forming.
U.S. Pat. No. 3,843,346 and U.S. Pat. No. 3,884,665, both to Edge and Kunkle, describe the delivery of molten glass directly over a refractory support onto molten metal. U.S. Pat. No. 4,062,666 to Tilton and U.S. Pat. No. 4,055,407 to Heithoff and Pecoraro illustrate apparatus for delivering molten glass from a refractory glass support onto molten metal.
According to the teachings of these patents, a preferred refractory material to serve as a glass support member for delivery of molten glass onto molten metal is one comprising silica. The two patents to Tilton and to Heithoff et al. specifically suggest that the silica may be a fused quartz material.
It has been observed that fine bubbles or seeds occasionally occur in the bottom surface of glass produced by processes such as those described in the above-mentioned patents. These fine bubbles or seeds have been observed to occur most frequently immediately after the initiation of glass delivery and forming in newly constructed or repaired chambers. In the practice of the free-fall delivery method, the bubbles are generally concentrated in the marginal portions of the flat glass while they are more uniformly distributed throughout the bottom surface of flat glass produced following direct delivery without free fall. The present invention provides a method and apparatus for minimizing the incidences of bubbles or seeds in glass formed immediately after the initiation of glass forming in a forming facility and serves to increase the immediate productivity of a glass forming facility.